The prior art teaches that antioxidant activity in phenolic compounds occurs because of hydrogen extraction from the hydroxyl groups, see Scott, Atmospheric Oxidation of Antioxidants, Chapter IV (1965). It has been found according to the present invention that esterification of phenolic compounds and a subsequent reaction with a mercaptophenol produces an antioxidant with significantly enhanced antioxidant activity.
It is known that essentially all types of organic polymers, both natural and synthetic, and particularly rubbers from dienes are susceptible to deterioration resulting from prolonged exposure to oxidative aging. Unfortunately many of the commercially used stabilizers are often volatilized when the polymeric products are exposed to elevated temperature and/or high vacuum over a prolonged period of time. Furthermore, these known antioxidants are rather quickly extracted from polymeric compositions by repeated washing with aqueous detergent solutions or organic solvents. These severe conditions are routinely encountered by rubberized garments or garments containing rubber when they are subjected to frequent laundering or dry cleaning.
Attempts to remedy these problems are disclosed in references such as U.S. Pat. Nos. 3,714,122; 3,952,402; 3,962,187; 3,645,970; 3,305,552; 3,699,172; 3,728,399; 3,984,372; German Pat. No. 1,931,452, Canadian Pat. No. 955,349 and Canadian Pat. No. 979,594. U.S. Pat. No. 3,553,163 took a prior art compound 4-methylthiol phenol and discovered that by placing a substituent on a ring he could improve the antioxidative activity of the compounds. None of these references, however, discloses or suggests the use of polyphenolic esters of mercaptophenols as antioxidants for organic compositions which tend to deteriorate by absorption of oxygen. Thus, it is evident that polyphenolic antioxidants which provide solutions to the problems of antioxidant extraction and low antioxidative activity would be an advancement over presently known antioxidants.